U.S. News & World Report

Norovirus, rotavirus and viral gastroenteritis — commonly known as stomach flu — have a lot in common. All caused by viruses, they can lead to a world of gastrointestinal distress. Stomach flu may actually be caused by a variety of viruses including norovirus, rotavirus and others.

The conditions spread in similar ways and have certain key symptoms, particularly diarrhea, in common. However they vary in how long illness lingers and possible consequences depending on the age of the person affected. And now, they can also share some GI side effects with another viral infection, the relative newcomer called COVID-19.

As common infectious diseases go, norovirus is fast and furious. “It usually comes on quickly (and) suddenly with vomiting and diarrhea,” says Dr. Jason Newland, a pediatric infectious disease doctor at St. Louis Children’s Hospital and a professor of pediatrics at Washington University School of Medicine. “It lasts about 24 to 60 hours for normal healthy people, and it doesn’t take a lot of this virus to cause you to get sick.”

In fact, norovirus is the leading cause of diarrheal illness in the U.S. among adults. According to the Centers for Disease Control, 21 million cases are reported each year, with most outbreaks happening from November to April. Young children, older adults and people with chronic medical conditions are at higher risk for more severe or persistent norovirus infection.

[READ: Getting to the Bottom of Diarrhea.]

Rotavirus illness used to present a formidable threat to infants and young children, and still does in some parts of the world. Kids infected with rotavirus could become extremely sick with severe vomiting and watery diarrhea, resulting in devastating dehydration leading to hospitalization and even death. According to the World Health Organization, five rotavirus strains cause the bulk of human rotavirus disease.

“The big, revolutionary change in rotavirus is the development of the vaccine,” says Dr. Robin Colgrove, an infectious disease doctor at Mount Auburn Hospital in Cambridge, Massachusetts, and an assistant professor of medicine at Harvard Medical School. “Now that most of the kids in developed countries are vaccinated, we see many fewer cases.” Cases that do occur where vaccination is widespread tend to be far less severe than in the past.

Currently, two rotavirus vaccines — RotaTeq and Rotarix — are available in the U.S. Both are given as oral drops, with either a two- or three-dose series, typically completed in infancy.

However, “It’s still a huge deal in the world as a whole because it’s a major killer of very small children,” Colgrove adds. Diarrhea from rotavirus illness may cause fluid loss in large proportions to a child’s total body weight, and in some areas there can be challenges in accessing essential treatment with intravenous fluids.

In the U.S., children in settings like day care centers with many young children, are at most risk for rotavirus infection, according to the Centers for Disease Control and Prevention. The worst disease occurs among unvaccinated children from the ages of 3 months to 3 years old.

Older adults, those who are immunocompromised or who take care of kids with rotavirus disease are also at higher risk of getting rotavirus.

[Read: Stomach Flu vs. Food Poisoning: How to Recognize the Difference]

What Is Stomach Flu (Gastroenteritis)?

When the symptoms of norovirus or rotavirus hit, those affected often refer to their affliction as the “stomach flu.” Yet the term is a misnomer, as none of these is caused by a flu virus.

Instead, stomach flu — more correctly known as gastroenteritis — generally refers to an irritation of the stomach or gastrointestinal tract, which can cause diarrhea, vomiting and stomach pain.

“Many, many viruses and many bacteria can result in symptoms that someone would describe as a stomach flu — which can be misleading,” says Dr. Lukasz Weiner, a pediatric infectious disease doctor at University of Iowa Hospitals and Clinics. He prefers the term gastroenteritis. “I think it’s a more accurate term medically. But I know people use the term stomach flu to describe something similar.”

[SEE: Best Foods to Eat for an Upset Stomach.]

How Norovirus and Rotavirus Spread

Norovirus and rotavirus are, in the medical parlance, both spread by what’s called fecal-oral transmission. That is to say there’s no getting around the disgusting way these highly contagious diarrheal illnesses are rapidly passed from one victim to the next.

“The transmission is out the rectum of one person and in the mouth of somebody else,” Colgrove explains “So they’re transmitted by stool.” Even microscopic bits of stool from watery diarrhea can carry the virus.

It’s also a hardy virus, Newland adds. They will linger on counter surfaces. Unsanitary conditions further fuel the spread of these infectious diseases. In developing parts of the world, they are typically spread via the water supply. In contrast, in the U.S. and other developed countries, they’re commonly spread when people are in close quarters, like day care centers, hospitals and cruise ships.

They can also be spread through food preparation. In fact, norovirus is a leading cause foodborne illness. That’s led to restaurants grappling with headline-grabbing outbreaks of the hard-to-shake disease.

The Difference Between Norovirus and Rotavirus

Medical experts say it’s difficult, if not impossible, to be able to distinguish between norovirus and rotavirus based on symptoms alone. For each those include:

The primary differences between norovirus and rotavirus are based on who gets it, how long the infection typically lasts and the possible complications. The norovirus typically lasts no more than about two and a half days, while rotavirus generally lasts three to eight days. Because rotavirus typically affects babies and young children, that loss of fluid is more significant than it would be for adults. Severe dehydration, especially for infants and young children, can be life threatening.

While kids can get norovirus too, this virus is seen more in adults. “Norovirus is the most common cause of acute diarrhea in adults in developed countries,” Colgrove says. This is different from diarrhea from chronic conditions like inflammatory bowel disease or that’s caused by a bug someone picked up from traveling abroad.

Rotavirus, on the other hand, was the most common cause of acute diarrheal illness in children in the world before vaccination against the disease was available. “Before we had a vaccine for it, there were millions of hospitalizations and hundreds of thousands of deaths per year among young children,” Colgrove says. Now highly effective infant vaccines provide protection against it. So while some kids do still get rotavirus in the U.S., illnesses and hospitalizations have plummeted as a result of routine vaccination.

Although norovirus generally passes more quickly, the infectious disease can linger in more vulnerable populations, like older adults who have other health issues. “The main complication of either of these infections is severe dehydration — which is the main reason that young children or the elderly, for example, require hospitalization,” Weiner says.

Adults who’ve had rotavirus as children, typically develop a lifelong immunity to it. But with norovirus, a person can get infected repeatedly. It’s harder for the body to build up a defense against it because the virus is much more prone to change or mutate. (There’s no vaccine for norovirus.)

In many cases, there’s little to do but endure the symptoms of norovirus, rotavirus or gastroenteritis until they pass. Clinicians say no proven cures or effective treatments exist to reliably reduce the duration of these diseases or significantly ease symptoms.

That said, experts emphasize the importance of hydration, including consuming electrolytes, while sick with norovirus or rotavirus. Rehydration drinks like Pedialyte may help to prevent the more serious complication of dehydration.

Regularly hydrating can prevent a dangerous loss of body fluids. “That’s the key to keeping people out of the hospital,” Newland says. “But sometimes (with) these little babies, it’s just too hard because they have so much vomiting and diarrhea.” That makes vaccination against rotavirus all the more critical.

Anti-diarrheal medications are typically not advised for children as these can actually make it harder for the body to rid itself of the virus.

Encouraging your child to rest, or getting rest if you’re the patient, is also important as both the illness and dehydration can make people feel tired and weak.

Because there are various illnesses that can cause gastrointestinal distress, it’s important not to assume that what you have is, say, norovirus. And be alert to escalating symptoms that may signal you need to be seen right away by a health care provider.

Adults and kids shouldn’t have a high fever with rotavirus or norovirus.

Viral gastroenteritis often causes low-grade fevers of typically less than 101.5 Fahrenheit in adults, Colgrove says. “High fevers greater than 102.5 F, particularly with shaking chills, is more suggestive of bacterial infections such as salmonellosis, which may require antibiotics.”

Colgrove adds that with kids, it’s more complicated. “They can run quite high fevers even with otherwise mild infections,” though usually not with shaking chills, he notes. “Parents of children with fever greater than 102 F should call their pediatrician and describe the symptoms, so they can get advice on whether to bring the child in to be evaluated.”

Symptoms in babies tend to be subtler, so it’s important for parents to monitor infants and young children even more closely. Contact your pediatrician right away if you have a concern about symptoms including fever.

Colgrove says high fever is one of several “alarm symptoms,” a medical term referring to things that could indicate a potentially serious problem. Here are other alarm symptoms to look out for:

— Not being able to take in as much fluids as you’re losing.

— Blood in your vomit or diarrhea.

For these or any other concerning symptoms, seek immediate medical attention.

For anyone who has norovirus or rotavirus, experts reiterate the importance of regular hand-washing and not making a hasty return to work or life outside your home. Wait until you’re healthy again, so you don’t give one of these highly infectious diseases to someone else.

COVID-19 is infamous for devastating respiratory effects such as shortness of breath and severe pneumonia that overwhelmed intensive care units, put many patients on ventilators and too often resulted in death.

However, COVID-19 can also cause GI symptoms, along with the respiratory symptoms or alone. People with COVID-19 may experience stomach pain, diarrhea, nausea and vomiting, and appetite loss.

Early in the pandemic, this further complicated diagnosis of GI conditions, which might be due to norovirus, rotavirus or COVID-19, among other causes. Today, testing makes it somewhat easier to sort out the cause.

“The home testing for SARS-CoV-2, or COVID-19, has really made testing more accessible,” Colgrove says. “Unfortunately, we don’t have anything similar for norovirus.”

In fact, “A very large majority of people with diarrheal illness don’t get any diagnosis,” Colgrove says, and when tests are done, everything may come up negative. “Really, the most common thing is that people get diarrhea, they get better and we never really identify it.”

The most important thing anyone can do to protect against the spread of norovirus — and rotavirus, apart from vaccination for that disease — is hand-washing, experts say. The best method for hand-washing is actually simply using soap and water.

“The alcohol gels aren’t as effective,” Newland says. You won’t likely inactivate these sturdy viruses. And you don’t want to use gels that remain on your hands. Instead, Colgrove notes, you want to wash the viruses down the drain.

When washing your hands, be sure to scrub thoroughly for at least 20 seconds, the CDC suggests. Additionally, clean surfaces, make sure you always wash food and don’t prepare food at all when you’re sick with a diarrheal illness.

“COVID-19 has made us take contagious illness seriously in the way that we probably always should have,” Colgrove says. Not sneezing or coughing on people when you’re sick, wearing a mask, social distancing, washing your hands properly and staying home rather than gutting it out while you’re sick can help prevent the spread of many contagious conditions. “Hopefully, we can hold onto some of that hard-earned wisdom from the pandemic,” he says.

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Rotavirus, Norovirus or Stomach Flu: What?s the Difference? originally appeared on usnews.com

Update 05/20/22: This story was previously published at an earlier date and has been updated with new information.

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